Zip Lock Plastic Bag are plastic sacks or pouches that have an interlocking or slide lock closure mechanism. Such a device allows for a waterproof, airtight seal as is desired in many applications to further protect and better contain goods. Popular for home, office and industrial use, zip lock bags are manufactured and distributed by several recognizable companies as well as smaller brands providing accessible and affordable options for all plastic bag sealing needs.

Food, archival, parts, shipping and storage industries are among the most fervent users of zip lock bags. To accommodate the many uses for zip lock or lock top bags, most manufacturers produce them in several different standardized sizes. Common domestic sizes include snack, sandwich, quart and gallon bags. Industrial bags are often much larger while other archival baggies are often very small. As a secure seal is essential, some bags have two different colored seams which are easily identified when open and become a different color when the closure is properly sealed. Common alternatives include the use of twist ties and heat-sealed or shrink-wrapped bags. Twist ties are useful, but do not provide the durable and impermeable seal of the zipper lock. Heat-sealed or shrink-wrapped options create an effective seal, but are not reclosable or resealable bags as zip lock bags may be.

Not all, but most zip lock bags are made to be resealed and even reused any number of times. Durable materials must therefore be used in the construction of both the bag and attached locking devices. Polypropylene and polyethylene are most frequently used for the film-like bag component. The plastic resin is melted until it becomes pliable or even to temperatures which produce a viscous fluid. Casting, winding, sheet or blown film extrusion may then be used. The seal is formed in a mold. Thicker, stronger plastic is used, though it may have a base material similar to that used for the film. A male track is fixed to one side of the opening of the bag while the female track is placed parallel on the adjacent edge. The tracks connect together like puzzle pieces when pressure is applied either manually or through the use of a plastic slider. The fastening capabilities vary among the many manufacturers of zip lock bags, but all require a significant tug to part the closure of a properly sealed bag. It is important to consider the durability of a seal as well as the plastic material used in overall bag construction to ensure the proper unit is used.